This invention relates to improvements in methods for casting a reinforced concrete pile in the ground, and particularly to a method for casting a partially reinforced concrete pile which is reinforced in its upper portion against side-loading from earthquakes, wind and other influences.
It has long been known to cast concrete piles in the ground, either without exterior reinforcing casings as exemplified by DeWitt U.S. Pat. No. 4,992,002, or with full-length exterior reinforcing casings as exemplified by DeWitt U.S. Pat. No. 5,419,658. When no permanent exterior reinforcing casing is provided, reinforcement against side-loading from earthquakes, wind and other influences is normally supplied by means of a steel cage assembly composed of reinforcing bars embedded in the concrete of the pile. However it is often difficult to position such a cage assembly centrally in the pile accurately enough to ensure sufficient resistance to side-loading from all lateral directions, and to provide adequate cover of the steel bars as called for in all building codes. Moreover, even if accurate positioning of the cage assembly were obtainable, its central location within the pile would not provide resistance to lateral beam stresses nearly as effectively as reinforcement located at the exterior surface of the pile. Another drawback of piles which are cast in a hole without a permanent exterior casing is that excess concrete grout must normally be pumped at the top of the hole to prevent its collapse, thereby adding to the cost of material for each pile.
The use of a full-length exterior reinforcing casing in conjunction with a cast-in-place pile is also problematic. The need to leave such a casing, usually of expensive steel construction, permanently in the ground to provide the reinforcement, coupled with the significant length of the casing, makes the cost of material for each pile excessively high. In addition, due to the poor surface friction of such a smooth casing relative to the soil, the casing must usually be driven until it reaches dense end-bearing strata in order to provide sufficient support. In contrast, the very high surface friction of a concrete pile allows for a much shorter pile, with less cost of material and less driving time.
What is needed, therefore, is a method for in-ground casting of concrete piles having reliably positioned, highly-effective reinforcement against side-loading, while minimizing the cost of material, equipment and/or time for the formation of each pile.
The foregoing and other objectives, features, and advantages of the invention will be more readily understood upon consideration of the following detailed description, taken in conjunction with the accompanying drawings.